Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Sun Jun 23 2019
Valid 12Z Thu Jun 27 2019 - 12Z Mon Jul 01 2019
Models are starting to hint at a pattern change across Alaska by
next weekend with a potential breakdown of the upper ridge,
opening mainland Alaska up to stronger and more active westerly
mid/upper-level flow. Before that occurs, models show improved
agreement during the early part of the extended period on a
weakening frontal system crossing the eastern Aleutians. The
majority of upper-level energy associated with this system should
be deflected either north toward eastern Russia or south into the
northern Pacific due to the upper ridge anchored over western
mainland Alaska at that time. A blend of the ECMWF and GFS served
as a starting point for the forecast on day 4 (Thu) with a 50/50
deterministic/ensemble blend on day 5 (Fri). After that, spread
increases quite a bit with the GFS ejecting another shortwave east
across the Bering Sea, and breaking down the upper ridge much more
quickly than the ECMWF/CMC. At this time a trend toward ensemble
means was preferred during days 6-8 (Sat-Mon), which does break
down the ridge at least a day slower than the GFS. This solution
should allow shortwave energy and an associated surface frontal
system to reach mainland Alaska on Sun, pushing inland by Mon as
it weakens. This setup would bring an end to the drier conditions
seen across much of Alaska recently, with an increase in
moisture/showers especially for southern mainland Alaska.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html